As far as we are concerned, filters have to be very
free flowing, but not necessarily all that effective
at filtering dust..

An unfiltered automotive engine will seize up in a
sand storm, but if our scopes ever see such an
environmental attack we probably have far bigger
problems.

For us, a little dust, though annoying, really isn't all
that harmful. A little blow down with compressed air,
and it will look like new. The bigger dust, hairballs,
mice and insects are what we have to be careful to filter.

HP for years used pleated aluminum window screen filters with
a little added sticky stuff to enhance their effectiveness.

I think we should aim for that level of performance.

The old style coated aluminum mesh filters were slightly better
than that, and were very free flowing.

There are furnace filters available that are like a coated
horse hair mat. I have used them to good affect to replace
the foam filters on 545B's and 547's... though I still tend
to look for the aluminum mesh variety.

If you choose to use one of the furnace filters, be warned
that not all 500 series scopes have a piece of diamond screen
to protect the fan. Early scopes (585A) with the aluminum mesh
filter may not have that feature. You must be sure it is
there if you are going to use a furnace filter, or your fan
will get stopped.

-Chuck Harris

Jack wrote: